Quantum efficiency of multiple quantum wells

ABSTRACT

Improved quantum efficiency of multiple quantum wells. In accordance with an embodiment of the present invention, an article of manufacture includes a p side for supplying holes and an n side for supplying electrons. The article of manufacture also includes a plurality of quantum well periods between the p side and the n side, each of the quantum well periods includes a quantum well layer and a barrier layer, with each of the barrier layers having a barrier height. The plurality of quantum well periods include different barrier heights.

FIELD OF INVENTION

Embodiments of the present invention relate to the field of integratedcircuit design and manufacture. More specifically, embodiments of thepresent invention relate to systems and methods for improved quantumefficiency of multiple quantum wells.

BACKGROUND

Multiple quantum well (MQW) structures are in wide use in light emittingdiodes and diode lasers, including visible-wavelength lasers for DVDsand laser pointers, lasers in fiber optic transmitters and blue lightemitting diodes, which form the basis of many “white” light emittingdiodes. Multiple quantum wells are also used to make HEMTs (HighElectron Mobility Transistors), which are used in low-noise electronics.Quantum well infrared photodetectors are also based on quantum wells,and are used for infrared imaging. Further, multiple quantum wellstructures are utilized in some photo-voltaic (solar) cells.

Increased quantum efficiency of such devices is desired.

SUMMARY OF THE INVENTION

Therefore, what is needed are systems and methods for improved quantumefficiency of multiple quantum wells. What is additionally needed aresystems and methods for improved quantum efficiency of multiple quantumwells that improve the recombinational efficiency of spatially diversequantum well structures. A further need exists for systems and methodsimproved quantum efficiency of multiple quantum wells that arecompatible and complementary with existing systems and methods ofintegrated circuit design, manufacturing and test. Embodiments of thepresent invention provide these advantages.

In accordance with an embodiment of the present invention, an article ofmanufacture includes a p side for supplying holes and an n side forsupplying electrons. The article of manufacture also includes aplurality of quantum well periods between the p side and the n side,each of the quantum well periods includes a quantum well layer and abarrier layer, with each of the barrier layers having a barrier height.The plurality of quantum well periods include different barrier heights.

In accordance with another embodiment of the present invention, anarticle of manufacture includes a p side for supplying holes and an nside for supplying electrons. The article of manufacture also includes aplurality of quantum well periods between the p side and the n side,each of the quantum well periods including a quantum well layer and abarrier layer, with each of the barrier layers having a p type dopingconcentration. The plurality of quantum well periods include barrierlayers with different p type doping concentrations.

In accordance with an additional embodiment of the present invention, anarticle of manufacture includes a multiple quantum well light emittingdiode including a plurality of quantum well periods. Each of the quantumwell periods includes a quantum well layer and a barrier layer. Each ofthe quantum well layers includes a quantum well layer thickness and aquantum well layer area. Each of the barrier layers includes a barrierlayer thickness, a barrier height, a barrier layer area and a barrierlayer p-doping concentration. At least one of the barrier height, thequantum well layer area, and the barrier layer p-type dopingconcentration vary across the plurality of quantum well periods suchthat quantum well efficiency is improved in comparison to a device inwhich the barrier height, the quantum well layer area and the barrierlayer p-type doping concentration are constant across the plurality ofquantum well periods.

In accordance with a method embodiment of the present invention, amethod includes forming a stack of layers for a multiple quantum wellsemiconductor device on a substrate. The stack of layers includes a ptype layer, an electron blocking layer in contact with the p type layer,and a plurality of quantum well periods in contact with the electronblocking layer. Each of the quantum well periods includes a quantum welllayer and a barrier layer. The stack of layers also includes an n-typelayer in contact with the plurality of quantum well periods. The methodfurther includes etching the stack of layers such that the plurality ofquantum well periods include quantum well layers of varying area.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention. Unless otherwise noted, the drawings are not drawn to scale

FIG. 1A illustrates an energy band diagram of a light emitting diode, inaccordance with embodiments of the present invention.

FIG. 1B illustrates a different energy band diagram of a light emittingdiode, in accordance with embodiments of the present invention.

FIG. 2 illustrates an exemplary p-type doping profile for a multiplequantum well (MQW) light emitting diode, in accordance with embodimentsof the present invention.

FIG. 3 illustrates a side-sectional view of an exemplary multiplequantum well (MQW) light emitting diode device, in accordance withembodiments of the present invention.

FIGS. 4A and 4B illustrate an exemplary method of forming a multiplequantum well light emitting diode (MQW LED), in accordance withembodiments of the present invention.

FIGS. 4C and 4D illustrate an exemplary method of forming a multiplequantum well light emitting diode (MQW LED), in accordance withembodiments of the present invention.

FIG. 5 illustrates an example of an application of multiple quantum welllight emitting diodes having improved quantum efficiency, in accordancewith embodiments of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withthese embodiments, it is understood that they are not intended to limitthe invention to these embodiments. On the contrary, the invention isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the invention as defined bythe appended claims. Furthermore, in the following detailed descriptionof the invention, numerous specific details are set forth in order toprovide a thorough understanding of the invention. However, it will berecognized by one of ordinary skill in the art that the invention may bepracticed without these specific details. In other instances, well knownmethods, procedures, components, and circuits have not been described indetail as not to unnecessarily obscure aspects of the invention.

Notation and Nomenclature

Some portions of the detailed descriptions which follow (e.g., process400 and 401) are presented in terms of procedures, steps, logic blocks,processing, and other symbolic representations of operations on databits that may be performed on computer memory. These descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. A procedure, computer executed step, logicblock, process, etc., is here, and generally, conceived to be aself-consistent sequence of steps or instructions leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated in a computersystem. It has proven convenient at times, principally for reasons ofcommon usage, to refer to these signals as bits, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing terms such as “attaching” or “processing” or“singulating” or “processing” or “forming” or “roughening” or “filling”or “accessing” or “performing” or “generating” or “adjusting” or“creating” or “executing” or “continuing” or “indexing” or “processing”or “computing” or “translating” or “calculating” or “determining” or“measuring” or “gathering” or “running” or the like, refer to the actionand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

Although exemplary embodiments in accordance with the present inventionare illustrated in terms of a gallium nitride light emitting diode, suchexamples are not limiting. It is to be appreciated that embodiments inaccordance with the present invention are well suited to a variety ofdevices employing multiple quantum wells, employing a variety ofmaterials.

Improved Quantum Efficiency of Multiple Quantum Wells

In silicon or most III-V compound semiconductors such as galliumarsenide (GaAs), gallium phosphide (GaP) or gallium nitride (GaN), themobility of holes as charge carriers is less than that of electrons. Forexample, holes have a larger effective mass than electrons. In addition,for example in a light emitting diode, holes are less efficientlyinjected through an electron blocking layer (EBL), in comparison withelectrons. Thus, there may be many more electrons than holes in anactive MQW region, resulting in a charge imbalance.

Accordingly, excessive electrons in an active region may quench “useful”electron-hole pairs which would otherwise contribute to light outputthrough radiative recombination. Further, electrons may overflow out ofa quantum well without contributing to radiative recombination in anactive region. Accordingly, excessive and/or leaking electronsdetrimentally decrease a device's quantum efficiency at increasedcurrent density (known as the “droop” problem), which deters wideadoption of MQW devices in important applications, e.g., area lighting,under the conventional art.

FIG. 1A illustrates an energy band diagram 100 of a light emittingdiode, in accordance with embodiments of the present invention. The Xdimension indicates position in space, which may be, for example, thedistance from a substrate, also known as the direction of growth. The Ydimension indicates electron energy, e.g., measured in electron volts(eV). The light emitting diode comprises a multiple quantum well (MQW).In contrast with the conventional art, the well thickness, barrier layerthickness and/or barrier height, e.g., electron energy of a barrierlayer, are not uniform among the plurality of wells.

For example, wells 123, 125, 135, 145, 155 and 165 are characterized ashaving different thicknesses. Similarly, barrier layers 120, 130, 140,150 and 160 are characterized as having different thicknesses. Inaddition, barrier layers 120, 130, 140, 150 and 160 are characterized ashaving different heights, e.g., different electron energies. Inaccordance with embodiments of the present invention, well thicknessincreases from the n layer, e.g., the cathode, to the p layer, e.g., theanode. Similarly, barrier height increases from the n layer, e.g., thecathode, to the p layer, e.g., the anode. It is appreciated that thebarrier layer thickness decreases from the n layer, e.g., the cathode,to the p layer, e.g., the anode.

It is appreciated that embodiments in accordance with the presentinvention are well suited to non-uniformity in one or more aspects of aplurality of quantum wells. For example, in some embodiments, only wellthickness may be changed. In other embodiments, only barrier layerthickness may be changed. In still other embodiments, only barrierheight may be changed.

Further, embodiments comprising changes to only two aspects ofnon-uniformity across a plurality of quantum wells are possible. Forexample, in some embodiments, well thickness and barrier layer thicknessmay be changed, while barrier height is uniform. In other embodiments,well thickness and barrier height are changed, while well thickness isuniform. In still other embodiments, barrier height and well thicknessare changed, while barrier layer thickness is uniform. All suchcombinations are to be considered embodiments in accordance with thepresent invention.

The well layers of a multiple quantum well (MQW) region, e.g., of a blueLED, may comprise indium gallium nitride (InGaN). In an exemplaryembodiment, the well layers of a plurality of quantum wells may be madeof In_(0.15)Ga_(0.85)N, which emits a sky blue light with a wavelengthpeak at 475 nm. A barrier layer in a MQW may comprise GaN,In_(y)Ga_((1-y))N, Al_(x)Ga_((1-x))N or Al_(x)In_(y)Ga_((1-x-y))N. Theband gap of the barrier material may be adjusted by controlling itscomposition (x or y value), which leads to different barrier heights.This may be achieved, e.g., by controlling the mixing ratio of flowrates of the precursor gases into a metal organic chemical vapordeposition (MOCVD) chamber. If the well layer of MQW is made ofIn_(0.15)Ga_(0.85)N, then the barrier material can be chosen asIn_(y)Ga_((1-y))N, where 0<=y<0.15, leading to different band gap andthus a different barrier height.

In accordance with embodiments of the present invention, a lower barrierheight facilitates hole transport through the barrier layer.Accordingly, changing the energy band diagram across a MQW region, e.g.,as illustrated in FIG. 1, may make hole and electron distribution morebalanced within a MQW, beneficially recombining holes more efficientlywith electrons, reducing an excess of electrons, and thus improvingquantum efficiency of multiple quantum wells.

It is to be appreciated that not all well layers have to have differentthicknesses, not all barrier layers have to have different thicknesses,and not all barrier layers have to have different heights, in accordancewith embodiments of the present invention. For example, FIG. 1Billustrates an energy band diagram 100B of a light emitting diode, inaccordance with embodiments of the present invention. In comparison withFIG. 1A, FIG. 1B illustrates that not all well thicknesses, barrierthicknesses and barrier heights change in each period of a multiplequantum well structure.

For example, barrier 150B has the same barrier height and thickness asbarrier 140, and well 155B has the same thickness as well 145. Eventhough every period does not change, energy band diagram 100Billustrates that well thickness generally increases from the n layer,e.g., the cathode, to the p layer, e.g., the anode. Similarly, barrierheight generally increases from the n layer, e.g., the cathode, to the player, e.g., the anode, while the barrier layer thickness generallydecreases from the n layer, e.g., the cathode, to the p layer, e.g., theanode.

FIG. 2 illustrates an exemplary p-type doping profile 200 for a multiplequantum well (MQW) light emitting diode, in accordance with embodimentsof the present invention. A p-doing concentration, e.g., doping withmagnesium (Mg), may be varied from one barrier layer to another across aplurality of quantum wells. For example, a first barrier region closestto an n side of a light emitting diode may have a first concentration ofp-doping. A next barrier region may have a decreased concentration ofp-doping relative to the first barrier region. In general, a p-doingconcentration for each successive barrier region, from n side to p side,should decrease. As with the embodiment of FIG. 1A, each barrier regionis not required to have a different p type doping concentration.

As illustrated in FIG. 2, a first barrier layer, closest to the n-GaNlayer, has an exemplary p-doing concentration 210. A next barrier layer,adjacent to the first barrier layer and farther from the n-GaN layer,has an exemplary p-doing concentration 220. P-doping concentrations 230,240 and 250 correspond to barrier layers successively farther away fromthe n-GaN layer. Exemplary p-doping concentration 250 indicates a dopingconcentration for a barrier closest to the electron barrier layer (EBL)and the p-GaN layer. This may be achieved, e.g., by controlling themixing concentration of flow rates of the precursor gases into a metalorganic chemical vapor deposition (MOCVD) chamber. It is appreciatedthat the change in p-doping concentration between successive barrierlayers need not be consistent or linear, in accordance with embodimentsof the present invention.

In accordance with embodiments of the present invention, suchnon-uniform doping across a multiple quantum well (MQW) region may causea more uniform distribution of holes across a plurality of quantumwells, beneficially recombining holes more efficiently with electrons,reducing an excess of electrons, and thus improving quantum efficiencyof multiple quantum wells.

It is to be appreciated that the novel non-uniform p-doping of anmultiple quantum well (MQW) structure illustrated in the exemplaryembodiment of FIG. 2 may be applied to an otherwise uniform multiplequantum well region, e.g., a multiple quantum well region in which wellthickness, barrier thickness and barrier heights are uniform across themultiple quantum wells. The novel non-uniform p-doping of an otherwiseuniform MQW may still improve hole distribution, increase hole andelectron recombination, and improve quantum efficiency of an LED, inaccordance with embodiments of the present invention.

In accordance with embodiments of the present invention, the embodimentsof FIGS. 1A and/or 1B and FIG. 2 may be combined. For example, withreference to both FIGS. 1A and/or 1B and FIG. 2, the p-doping level ofbarrier layer 120 may be doping level 210, the p-doping level of barrierlayer 130 may be doping level 220, and so on.

In accordance with embodiments of the present invention, the non-uniformwell and barrier structure, and non-uniform doping profile of aplurality of quantum wells promotes charge balance, e.g., the numbers ofholes and electrons are similar. Thus, the efficiency of light emittingdiodes in accordance with embodiments of the present invention isincreased relative to the convention art devices.

FIG. 3 illustrates a side-sectional view of an exemplary multiplequantum well (MQW) light emitting diode device 300, in accordance withembodiments of the present invention. Layer 310 is a p-GaN layer. Layer320 is an electron blocking layer (EBL). Layer 390 is an n-GaN layer.Layers 330-380 are three “periods” of multiple quantum wells (MQW). Incontrast to the conventional art, the plurality of quantum wells are notuniform. For example, electron blocking layer 320 is wider than barrier330, barrier 330 is wider than well 340, well 340 is wider than barrier350, barrier 350 is wider than well 360, well 360 is wider than barrier370, barrier 370 is wider than well 380 and well 380 is wider than n-GaNlayer 390. It is appreciated that embodiments in accordance with thepresent invention are well suited to more or fewer periods of MQW.

It is appreciated that the edges of the various layers 330-380 need notbe straight, and need not be at a constant angle. For example, the edgesmay be curved. Further, the layers may form a stair step pattern, inwhich the edges are substantially vertical. Likewise, a barrier and itsassociated well may have the same horizontal dimensions, and a decreasein width (in the view of FIG. 3) may occur between “periods” of thequantum wells.

In general, the area, e.g., in plan view, of each quantum well layerdecreases from the p side to the n side. For example, each quantum wellperiod comprises a barrier layer and a quantum well layer. The area ofeither or both of a barrier layer and/or a quantum well layer may bevaried among periods, in accordance with embodiments of the presentinvention. It is appreciated that such a relatively larger area towardsthe p side of the light emitting diode may compensate for the relativelypoor transport of holes injected from the p side, and help to achieve abalance of holes and electrons within a plurality of quantum wells,thereby increasing quantum efficiency of the device.

It is to be appreciated that the embodiments of FIGS. 1A and/or 1Band/or FIG. 2 may be combined with embodiments of FIG. 3 in a variety ofcombinations to further balance holes and electrons within a pluralityof quantum wells, thereby increasing quantum efficiency of the device.

FIGS. 4A and 4B illustrate an exemplary method 400 of forming a multiplequantum well light emitting diode (MQW LED), in accordance withembodiments of the present invention. As illustrated in FIG. 4A, aGallium nitride (GaN) multiple quantum well (MQW) light emitting diodeis formed on a sapphire (α-Al₂O₃) substrate 405, via any suitableprocess and materials. For example, an n-type layer 490 of Galliumnitride (GaN) is formed on substrate 405. A three-period multiplequantum well structure 480-430 may be formed on the n-GaN layer 490.Layers 480, 460 and 440 are quantum well layers, and may comprise, forexample, indium gallium nitride (InGaN). Layers 470, 450 and 430 arebarrier layers, and may comprise, for example, gallium nitride GaN,indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN) oraluminum indium gallium nitride (AlInGaN).

A p-type layer 410 is formed on top of the MQW (480-430). As is typical,the diode structure is formed continuously over substantially all of thesapphire substrate, although this is not required. It is to beappreciated that embodiments in accordance with the present inventionare well suited to other types of devices comprising differentmaterials.

In FIG. 4B, portions of the layer stack are removed, in accordance withembodiments of the present invention. The material may be removed in anundercut via any suitable process, for example a wet etch employingalkaline etchants such as potassium hydroxide (KOH), with a controlledconcentration of etchant and buffering ions, time and temperature. It isappreciated that the general profile of the layers 410-480 in FIG. 4Bgenerally corresponds to the profile of layers set forth in FIG. 3. Forexample, the barrier and well layers increase in width—and area, in planview—from the n side to the p side.

FIGS. 4C and 4D illustrate an exemplary method 401 of forming a multiplequantum well light emitting diode (MQW LED), in accordance withembodiments of the present invention. As illustrated in FIG. 4A, aGallium nitride (GaN) multiple quantum well (MQW) light emitting diodeis formed on a sapphire (α-Al₂O₃) substrate 405, via any suitableprocess and materials. In contrast with the embodiment of FIG. 4A, thelayers are formed in the opposite order in the embodiment of FIG. 4C.For example, the p-GaN layer 410 is formed adjacent to the sapphiresubstrate 410, and the n-GaN layer 490 is formed on top of the stack.

In FIG. 4D, portions of the layer stack are removed, in accordance withembodiments of the present invention. The material may be removed viaany suitable process. It is appreciated that the general profile of thelayers 410-480 in FIG. 4D generally corresponds to the profile of layersset forth in FIG. 3. For example, the barrier and well layers increasein width—and area, in plan view—from the n side to the p side.

While the layer stack of the embodiment of FIGS. 4C and 4D, e.g., withthe p side against the substrate, may be less common than the layerstack of the embodiment of FIGS. 4A and 4B, e.g., with the n sideagainst the substrate, it may be advantageous to form the layers asillustrated in FIGS. 4C and 4D, in order to simplify the etchingprocess. For example, it may be more common, straight forward and/ormore controllable to etch as illustrated in FIG. 4D than to etch asillustrated in FIG. 4B.

In accordance with another embodiment of the present invention, multiplequantum wells of varying areas may be formed by a process of wet etchingafter nanoimprint patterning. For example, a low viscosity resist filmis pressed with a mold to create a thickness contrast in the resist. Theresist is then exposed to UV light, curing it to produce a rigid anddurable tightly bonded polymer network that conforms to the moldfeatures. The mold is separated from the polymer film, and the patterntransfer is completed using anisotropic etching to remove residue resistin the compressed troughs.

This nanoimprint lithography process is capable of defining a pattern ofnanoscale-size, e.g., less than about 100 nm, islands of resist/polymerserving as etch mask on the top surface of device stack of a single LED.Then the patterned LED wafer may be processed with a wet etch employingalkaline etchants such as potassium hydroxide (KOH) orTetramethylammonium hydroxide (TMAH), with a controlled concentration ofetchant and buffering ions, time and temperature, in order to achievethe desired profile of varying area throughout the thickness of MQW.After wet etching, resist and polymer film are stripped off with organicsolvent like acetone or N-Methyl-2-pyrrolidone (NMP) or an oxygen plasmaashing process. The spacing between etched LED islands may be filledwith dielectric materials such as SiO₂ and planarized to expose the topsurface of the LED stack so that a metal contact may be made bynanoimprint/metal deposition/liftoff and/or metaldeposition/nanoimprint/etching metal.

FIG. 5 illustrates an example of an application of multiple quantum welllight emitting diodes having improved quantum efficiency, in accordancewith embodiments of the present invention. Light appliance 500 is wellsuited to a variety of lighting applications, including domestic,industrial, automobile, aircraft and landscape lighting. Light appliance500 is also well suited to stage or theatrical lighting. Light appliance500 comprises a base 510. As illustrated, base 510 is an Edison typebase. It is appreciated that embodiments in accordance with the presentinvention are well suited to other types of bases, including, forexample, GU, bayonet, bipin, wedge, stage pin or other types of bases.

Light appliance 500 additionally comprises a body portion 520 thathouses power conditioning electronics (not shown) that convert 110 V ACinput electrical power (or 220 V AC, or other selected input electricalpower) to electrical power suitable for driving a plurality of lightemitting diode devices 540. Body portion 520 may also comprise, orcouple to, optional heat sink features (not shown).

Light appliance 500 may additionally comprise optional optics 530.Optics 530 comprise diffusers and/or lenses for focusing and/ordiffusing light from the plurality of light emitting diode devices 540into a desired pattern.

Light appliance 500 comprises a plurality of light emitting diodedevices. Individual LEDs of a plurality of light emitting diode devicesmay correspond to assemblies previously described herein. For examplelight appliance 500 may include one or more instances of a multiplequantum well light emitting diode. It is appreciated that not allinstances of light emitting diodes need be identical.

It is to be further appreciated that appliance 500 may comprise aplurality of individual, different, LED devices. For example, oneinstance of an electronic device may be a blue light emitting diodeformed on a sapphire substrate. Another instance of an electronic devicemay be a green light emitting diode formed on a gallium phosphide (GaP)substrate. Another instance of an electronic device may be a red lightemitting diode formed on a gallium arsenide (GaAs) substrate. The threeinstances of electronic devices may be arranged such that the light fromsuch three colors may be combined to produce a variety of spectralcolors. For example, a plurality of light emitting diode devices mayoperate in combination to produce a “white” light output.

In accordance with embodiments of the present invention, device 500 mayinclude additional electronics associated with the LED devices. In oneexemplary embodiment, such additional electronics may comprise circuitsto implement a white balance among tri-color LEDs.

Embodiments in accordance with the present invention provide systems andmethods for improved quantum efficiency of multiple quantum wells. Inaddition, embodiments in accordance with the present invention providesystems and methods for improved quantum efficiency of multiple quantumwells that improve the recombinational efficiency of spatially diversequantum well structures. Further, embodiments in accordance with thepresent invention provide for systems and methods improved quantumefficiency of multiple quantum wells that are compatible andcomplementary with existing systems and methods of integrated circuitdesign, manufacturing and test.

Various embodiments of the invention are thus described. While thepresent invention has been described in particular embodiments, itshould be appreciated that the invention should not be construed aslimited by such embodiments, but rather construed according to the belowclaims.

What is claimed is:
 1. An article of manufacture comprising: a p sidefor supplying holes; an n side for supplying electrons; and a pluralityof quantum well periods between said p side and said n side, each ofsaid quantum well periods comprising a quantum well layer and a barrierlayer, each said barrier layer having a barrier height, wherein saidplurality of quantum well periods comprise different barrier heights,wherein each said barrier layer has a barrier layer p type dopingconcentration, and wherein said plurality of quantum well periodscomprise different barrier layer p type doping concentrations.
 2. Thearticle of manufacture of claim 1 wherein said barrier height increasesfrom said n side to said p side.
 3. The article of manufacture of claim1 wherein said barrier height is different in each of said plurality ofquantum well periods.
 4. The article of manufacture of claim 1 whereinsaid barrier layer p type doping concentration decreases from said nside to said p side.
 5. The article of manufacture of claim 1 whereinsaid barrier layer p type doping concentration is different in each ofsaid plurality of quantum well periods.
 6. The article of manufacture ofclaim 1 wherein each said quantum well layer has a quantum well layerarea, and wherein said plurality of quantum well periods comprisequantum well layer areas.
 7. The article of manufacture of claim 6wherein said quantum well layer area increases from said n side to saidp side.
 8. The article of manufacture of claim 7 wherein said quantumwell layer area is different in each of said plurality of quantum wellperiods.
 9. The article of manufacture of claim 1 wherein each saidquantum well layer has a quantum well layer thickness, wherein saidplurality of quantum well periods comprise different quantum well layerthicknesses.
 10. The article of manufacture of claim 9 wherein saidquantum well layer thickness increases from said n side to said p side.11. The article of manufacture of claim 10 wherein said quantum welllayer thickness is different in each of said plurality of quantum wellperiods.
 12. The article of manufacture of claim 1 further comprising: abase for coupling to a source of alternating current; and electronicsfor converting said alternating current to direct current suitable foruse with a light emitting diode, and wherein said p side, said n sideand said plurality of quantum well periods form a portion of said lightemitting diode.
 13. An article of manufacture comprising: a multiplequantum well light emitting diode comprising a plurality of quantum wellperiods; each of said quantum well periods comprising a quantum welllayer and a barrier layer; each of said quantum well layers comprising aquantum well layer thickness and a quantum well layer area; each of saidbarrier layers comprising a barrier layer thickness, a barrier heightand a barrier layer p-doping concentration; and wherein at least one of:said barrier height, quantum well layer area, and said barrier layerp-type doping concentration vary across said plurality of quantum wellperiods such that quantum well efficiency is improved in comparison to adevice in which said barrier height, said quantum well layer area andsaid barrier layer p-type doping concentration are constant across saidplurality of quantum well periods, and wherein said barrier heightincreases from an n side to a p side of said multiple quantum well lightemitting diode.
 14. The article of manufacture of claim 13 wherein saidquantum well layer area increases from an n side to a p side of saidmultiple quantum well light emitting diode.
 15. The article ofmanufacture of claim 13 wherein said barrier layer p type dopingconcentration decreases from an n side to a p side of said multiplequantum well light emitting diode.
 16. The article of manufacture ofclaim 13 wherein said quantum well layer thickness increases from an nside to a p side of said multiple quantum well light emitting diode. 17.The article of manufacture of claim 13 wherein said barrier layerthickness decreases from an n side to a p side of said multiple quantumwell light emitting diode.
 18. The article of manufacture of claim 13further comprising: a base for coupling to a source of alternatingcurrent; and electronics for converting said alternating current todirect current suitable for use with said multiple quantum well lightemitting diode.